JP2007168717A - Pneumatic radial tire for off-road - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pneumatic radial tire for an off-road capable of accomplishing lighter weight compared with a conventional one while retaining traveling durability similar to the present one by exhibiting sufficient strength and rigidity as a carcass. <P>SOLUTION: The pneumatic radial tire for the off-road is provided with the carcass comprising at least two sheets of carcass plies 3; and a belt layer 5 comprising at least one sheet of belt ply. In the tire, at least one sheet of the carcass plies 3 comprises an organic fiber cord and coating rubber covering the organic fiber cord. The organic fiber cord comprises a polyketone fiber cord having a dry thermal shrinkage percentage of 1-10% at a temperature of 150°C. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to off-road pneumatic radial tires (hereinafter also simply referred to as “tires”) for construction vehicles and the like, and more specifically, enables weight reduction without impairing running durability, and reduces fuel consumption and transportation costs. The present invention relates to a pneumatic radial tire for off-road that can achieve suppression.

  In general, a pneumatic radial tire for heavy loads such as for off-road use a steel cord for a carcass ply. However, in recent years, particularly from the viewpoint of environmental protection and energy saving, there is a strong demand for weight reduction of tires, and high strength organic fiber cords that are lighter than steel cords have attracted attention.

From this point of view, polyketone fibers that are lighter than steel cords and that exhibit high elasticity and high fatigue resistance have attracted attention (for example, see Patent Document 1). From the same point of view, Patent Document 2 uses a carcass ply made of polyketone fiber and a coating rubber having predetermined physical properties to reduce the rigidity step between the cord and the rubber, and to achieve the same running durability as the current one. It has been reported that weight reduction can be achieved while maintaining.
JP 2000-141919 (Claims etc.) JP 2004-306631 A (Claims etc.)

  Although application of the polyketone fiber disclosed in the above-mentioned patent documents to the carcass ply has made it possible to reduce the weight of the tire, today it is desired to improve the performance with further weight reduction. For example, in order to obtain sufficient carcass strength using high-strength organic fibers such as aramid fibers instead of the conventional polyketone fibers, the number of cords driven per unit width of the cord is steel cord. It was necessary to increase the number of the carcass layers or to have two or more carcass layers. However, when the number of cords to be driven per unit width is increased, there is a problem that the crack progress at the end of the carcass ply is promoted and the running durability may be lowered.

  In addition, when the carcass layer is made up of two or more layers, the carcass cord cannot absorb the difference between the inner and outer diameters produced during tire manufacture, and the carcass cord on the inner surface side of the tire will be slackened, thereby exhibiting sufficient strength and rigidity. There was a problem that it could not be done or the durability was lowered.

  Therefore, an object of the present invention is to provide a pneumatic radial tire for off-road that can exhibit a sufficient strength and rigidity as a carcass and can achieve a lighter weight than ever while maintaining the same running durability as the current carcass. There is.

  As a result of diligent studies to solve the above problems, the present inventors have found that the above object can be achieved by using polyketone fibers satisfying predetermined physical property values in the carcass, and have completed the present invention. It was.

That is, the pneumatic radial tire for off-road according to the present invention is disposed on the outer side in the radial direction of the crown portion of the carcass including at least two carcass plies extending in a toroidal shape between a pair of bead cores, and at least 1 In a pneumatic radial tire for off-road comprising a belt layer composed of a plurality of belt plies, wherein at least one of the carcass plies is composed of an organic fiber cord and a coating rubber covering the organic fiber cord.
The organic fiber cord is composed of a polyketone fiber cord having a dry heat shrinkage of 1 to 10% at 150 ° C.

  In the present invention, the tensile strength of the polyketone fiber yarn is preferably 10 cN / dtex or more, and the tensile elastic modulus of the polyketone fiber yarn is preferably 200 cN / dtex or more. Furthermore, the dry heat shrinkage rate at 150 ° C. of the polyketone fiber cord is preferably 4 to 7%, and the carcass ply is preferably 3 to 5 sheets.

  According to the present invention, in a pneumatic radial tire for off-road, it is possible to realize sufficient strength and rigidity as a carcass and to achieve a lighter weight than ever while maintaining the same running durability as the current carcass. It becomes.

Hereinafter, embodiments of the present invention will be specifically described.
FIG. 1 is a cross-sectional view of an off-road pneumatic radial tire according to an embodiment of the present invention. As shown in FIG. 1, the tire 1 includes a pair of bead cores 2 (only one is shown in FIG. 1), at least two (four in the illustrated example) carcass plies 3, a reinforcing layer 4, and at least one ( The belt layer 5 is composed of six belt plies in the illustrated example. The carcass ply 3 includes a polyketone fiber (hereinafter abbreviated as “PK fiber”) cord according to the present invention, which will be described in detail below, and a coating rubber covering the PK fiber cord.

  In the carcass ply 3, a large number of PK fiber cords substantially extending in the tire radial direction are covered with a coating rubber. In the tire 1 of the preferred example shown in the figure, the carcass ply 3 has a carcass skeleton straddling the toroidal shape between the bead cores 2, and is wound around the bead cores 2 from the inside to the outside of the tire and then folded back and extended. It has a folded portion 3A.

  In order to obtain a desired effect, the carcass ply 3 is at least two, preferably 3 to 5. As shown in the drawing, each folded portion 3A is preferably covered from the outside of the tire with a reinforcing layer of steel cord or organic fiber cord at least at the end portion 3B.

  With such a reinforcing layer, it is possible to provide a bead portion reinforcing structure that relieves stress concentrated on the end portion 3B of the folded portion 3A and suppresses separation starting from the end portion 3B.

  The tire 1 of the preferred example shown in the figure is formed by arranging a belt layer 5 and a tread layer 7 outside the carcass ply 3 in the crown portion radial direction. The belt layer 5 has at least one belt ply. The belt layer 5 and the tread layer 6 are not particularly limited, and a known structure or the like for off-road use can be appropriately employed.

  In the present invention, the organic fiber cord applied to the carcass ply 3 is composed of a polyketone fiber cord having a dry heat shrinkage at 150 ° C. of 1 to 10%, preferably 4 to 7%. It is important to apply 3 at least 2, preferably 3-5. By making the dry heat shrinkage ratio 1% or more, it absorbs the difference between the inner and outer diameters that occur during tire manufacturing, expresses sufficient strength and rigidity as a carcass, and maintains the same running durability as the current, more than before. It becomes possible to achieve weight reduction. In addition, since the problem that the dimensional stability after vulcanization will deteriorate and the uniformity as a product will deteriorate when dry-heat shrinkage is too large, it is necessary to make it 10% or less.

  Moreover, the tensile strength of this PK fiber yarn is preferably 10 cN / dtex or more, more preferably 15 cN / dtex or more. As the tensile strength is higher, it can be used in fields where strength is required, and the weight of the fibers used can be kept low.

  Furthermore, the tensile elastic modulus is preferably 200 cN / dtex or more, more preferably 300 cN / dtex or more. The higher the tensile elastic modulus, the smaller the dimensional change under the same load, and the more excellent the shape stability.

Here, the dry heat shrinkage ratio is obtained by performing a dry heat treatment at 150 ° C. for 30 minutes on an unvulcanized PK fiber subjected to a general dip treatment, and the cord length before and after the heat treatment is 1/30 ( cN / dtex) is a value obtained by the following equation after measurement with a load.
Dry heat shrinkage (%) = (Lb−La) / Lb × 100
(However, Lb is the fiber cord length before heat treatment, and La is the fiber cord length after heat treatment.)

  The tensile strength and tensile modulus of the PK fiber yarn are values obtained by measurement according to JIS-L-1013, and the tensile modulus is the load and elongation of 0.1% at an elongation of 0.1%. It is the value of the initial elastic modulus calculated from the load at 2%.

  Specifically, the PK fiber cord used in the present invention is preferably a PK fiber cord described in detail below. That is, it is a multifilament twisted PK fiber having a total decitex per cord of 3000 to 17000 dtex. If the total decitex per one cord is in the range of 3000 to 17000 dtex, it is possible to achieve high rigidity and light weight compared to steel cord, which is an advantage of organic fibers. If the total decitex is less than 3000 decitex, sufficient high rigidity cannot be obtained as the carcass ply 3. On the other hand, if the total decitex exceeds 17000 decitex, the gauge of the carcass ply 3 becomes thick and tire mass increases.

Moreover, it is preferable that the PK fiber cord used in the present invention satisfies the relationship represented by the following formulas (I) and (II) in order to obtain the desired effect.
σ ≧ −0.01E + 1.2 (I)
σ ≧ 0.02 (II)
However, if σ is larger than 1.5, the shrinkage force during vulcanization becomes too large, resulting in the disorder of the cord inside the tire and the disorder of the rubber arrangement, which may lead to deterioration of durability and uniformity. As the upper limit,
1.5 ≧ σ
It is preferable to satisfy the relationship represented by these. Here, the heat shrinkage stress σ is obtained by heating a 25 cm long fixed sample of the PK fiber cord before vulcanization subjected to a general dip treatment at a heating rate of 5 ° C./min at 177 ° C. It is the stress (unit: cN / dtex) generated in the cord, and the elastic modulus E is the elastic modulus at 49 N load at 25 ° C. of the same PK fiber cord, and the SS curve of the JIS cord tensile test Elastic modulus of unit cN / dtex calculated from tangent at 49N.

In addition, the PK fiber cord further includes the following formula (III),
α = T × D ^1/2 (III)
(Where T is the number of twists (times / 100 mm) and D is the total fineness (dtex) of the cord), and the twist coefficient α is preferably in the range of 850 to 4000. If the twist coefficient α of the PK fiber cord is less than 850, the heat shrinkage stress cannot be secured sufficiently. On the other hand, if it exceeds 4000, the elastic modulus cannot be secured sufficiently and the reinforcing ability is reduced.

  Further, the PK fiber cord is preferably formed by twisting two or three filament bundles made of polyketone having a fineness of 1500 to 8500 dtex. If the fineness of the filament bundle used for the PK fiber cord is less than 500 dtex, both the elastic modulus and the heat shrinkage stress are insufficient. On the other hand, if it exceeds 3000 dtex, the cord diameter becomes thick and the driving cannot be made dense.

（式中、Ａは不飽和結合によって重合された不飽和化合物由来の部分であり、各繰り返し単位において同一であっても異なっていてもよい）で表される繰り返し単位から実質的になるものが好適であり、その中でも、繰り返し単位の９７モル％以上が１−オキソトリメチレン［−ＣＨ₂−ＣＨ₂−ＣＯ−］であるポリケトンが好ましく、９９モル％以上が１−オキソトリメチレンであるポリケトンが更に好ましく、１００モル％が１−オキソトリメチレンであるポリケトンが最も好ましい。 As a polyketone as a raw material of the PK fiber cord, the following general formula (IV),

(Wherein A is a portion derived from an unsaturated compound polymerized by an unsaturated bond, and may be the same or different in each repeating unit). Among them, a polyketone in which 97 mol% or more of the repeating units is 1-oxotrimethylene [—CH ₂ —CH ₂ —CO—] is preferable, and a polyketone in which 99 mol% or more is 1-oxotrimethylene. Is more preferable, and a polyketone in which 100 mol% is 1-oxotrimethylene is most preferable.

  In such polyketones, the ketone groups may be partially bonded to each other and the portions derived from the unsaturated compound may be bonded to each other, but the proportion of the portions in which the unsaturated compound-derived portions and the ketone groups are alternately arranged is 90 mass. % Or more, preferably 97% by mass or more, and most preferably 100% by mass.

  In the above formula (III), the unsaturated compound forming A is most preferably ethylene, but propylene, butene, pentene, cyclopentene, hexene, cyclohexene, heptene, octene, nonene, decene, dodecene, styrene, acetylene. , Unsaturated hydrocarbons other than ethylene such as allene, and methyl acrylate, methyl methacrylate, vinyl acetate, acrylamide, hydroxyethyl methacrylate, undecenoic acid, undecenol, 6-chlorohexene, N-vinylpyrrolidone, diethyl ester of sulphonylphosphonic acid Further, it may be a compound containing an unsaturated bond such as sodium styrene sulfonate, sodium allyl sulfonate, vinyl pyrrolidone and vinyl chloride.

（上記式中、ｔおよびＴは、純度９８％以上のヘキサフルオロイソプロパノールおよび該ヘキサフルオロイソプロパノールに溶解したポリケトンの希釈溶液の２５℃での粘度管の流過時間であり、ｃは、上記希釈溶液１００ｍＬ中の溶質の質量（ｇ）である）で定義される極限粘度［η］が、１〜２０ｄＬ／ｇの範囲内にあることが好ましく、３〜８ｄＬ／ｇの範囲内にあることがより一層好ましい。極限粘度が１ｄＬ／ｇ未満では、分子量が小さ過ぎて、高強度のポリケトン繊維コードを得ることが難しくなる上、紡糸時、乾燥時および延伸時に毛羽や糸切れ等の工程上のトラブルが多発することがあり、一方、極限粘度が２０ｄＬ／ｇを超えると、ポリマーの合成に時間およびコストがかかる上、ポリマーを均一に溶解させることが難しくなり、紡糸性および物性に悪影響が出ることがある。 Furthermore, as a polymerization degree of the said polyketone, following formula (V),

(In the above formula, t and T are the flow time of a viscosity tube at 25 ° C. of a diluted solution of hexafluoroisopropanol having a purity of 98% or more and a polyketone dissolved in the hexafluoroisopropanol, and c is the diluted solution. The intrinsic viscosity [η] defined by the mass (g) of solute in 100 mL) is preferably in the range of 1 to 20 dL / g, more preferably in the range of 3 to 8 dL / g. Even more preferred. If the intrinsic viscosity is less than 1 dL / g, the molecular weight is too small to obtain a high-strength polyketone fiber cord, and troubles such as fluff and yarn breakage occur frequently during spinning, drying and stretching. On the other hand, if the intrinsic viscosity exceeds 20 dL / g, it takes time and cost to synthesize the polymer, and it becomes difficult to uniformly dissolve the polymer, which may adversely affect the spinnability and physical properties.

  Furthermore, the PK fiber preferably has a crystal structure with a crystallinity of 50 to 90% and a crystal orientation of 95% or more. If the degree of crystallinity is less than 50%, the structure of the fiber is not sufficiently formed and sufficient strength cannot be obtained, and the shrinkage characteristics and dimensional stability during heating may be unstable. For this reason, the crystallinity is preferably 50 to 90%, more preferably 60 to 85%.

  The polyketone fiberization method includes (1) a method in which unstretched yarn is spun and then subjected to multistage hot stretching and stretched at a specific temperature and magnification in the final stretching step of the multistage hot stretching, (2 ) A method in which after the undrawn yarn is spun, hot drawing is performed, and the fiber after completion of the hot drawing is rapidly cooled with high tension applied. A desired filament suitable for the production of the polyketone fiber cord can be obtained by fiberizing the polyketone by the method (1) or (2).

  Here, the spinning method of the unstretched yarn of the polyketone is not particularly limited, and a conventionally known method can be employed. Specifically, JP-A-2-112413, JP-A-4-228613, Wet spinning method using an organic solvent such as hexafluoroisopropanol and m-cresol as described in JP-A-4-505344, WO99 / 18143, WO00 / 09611, JP2001 -164422, JP-A-2004-218189, JP-A-2004-285221, and the wet spinning method using an aqueous solution of zinc salt, calcium salt, thiocyanate, iron salt, etc. Among these, the wet spinning method using an aqueous solution of the above salt is preferable.

  For example, in a wet spinning method using an organic solvent, a polyketone polymer is dissolved in hexafluoroisopropanol, m-cresol, or the like at a concentration of 0.25 to 20% by mass, extruded from a spinning nozzle to be fiberized, and then toluene, ethanol, isopropanol The unstretched yarn of polyketone can be obtained by removing and washing the solvent in a non-solvent bath such as n-hexane, isooctane, acetone or methyl ethyl ketone.

  On the other hand, in the wet spinning method using an aqueous solution, for example, a polyketone polymer is dissolved in an aqueous solution of zinc salt, calcium salt, thiocyanate, iron salt or the like at a concentration of 2 to 30% by mass, and a spinning nozzle is formed at 50 to 130 ° C. Then, it is extruded into a coagulation bath and subjected to gel spinning, and further desalting and drying can be performed to obtain unstretched polyketone. Here, in the aqueous solution in which the polyketone polymer is dissolved, it is preferable to use a mixture of zinc halide and a halogenated alkali metal salt or a halogenated alkaline earth metal salt. An organic solvent such as an aqueous solution, acetone, or methanol can be used.

  Further, as a drawing method of the obtained undrawn yarn, a hot drawing method in which the undrawn yarn is heated and drawn to a temperature higher than the glass transition temperature of the undrawn yarn is preferable. The method (2) may be carried out in one stage, but it is preferably carried out in multiple stages. There is no restriction | limiting in particular as a method of heat drawing, For example, the method etc. which run a thread | yarn on a heating roll or a heating plate are employable. Here, the heat stretching temperature is preferably in the range of 110 ° C. to (melting point of polyketone), and the total stretching ratio is suitably 10 times or more.

  When polyketone fiberization is carried out by the method of (1) above, the temperature in the final stretching step of the multistage hot stretching is in the range of 110 ° C. to (the stretching temperature of the stretching step one step before the final stretching step). Moreover, the draw ratio in the final drawing step of multistage hot drawing is preferably in the range of 1.01 to 1.5 times. On the other hand, when polyketone fiberization is carried out by the method of (2) above, the tension applied to the fiber after completion of the hot drawing is preferably in the range of 0.5 to 4 cN / dtex, and the cooling rate in rapid cooling is 30 The cooling end temperature in the rapid cooling is preferably 50 ° C. or less. There is no restriction | limiting in particular as a rapid cooling method of the heat-stretched polyketone fiber, A conventionally well-known method can be employ | adopted, Specifically, the cooling method using a roll is preferable. In addition, since the polyketone fiber obtained in this way has a large residual elastic strain, it is usually preferable to perform relaxation heat treatment so that the fiber length is shorter than the fiber length after hot drawing. Here, the temperature of the relaxation heat treatment is preferably in the range of 50 to 100 ° C., and the relaxation ratio is preferably in the range of 0.980 to 0.999 times.

  The PK fiber cord is made of a multi-filament twisted PK fiber formed by twisting a plurality of the polyketone filaments. For example, the filament bundle made of the polyketone is subjected to a lower twist, and then two or three of them are combined. The twisted cord can be obtained by applying an upper twist in the opposite direction.

  In order to make the most effective use of the high heat shrinkage characteristics of PK fiber cords, the processing temperature during processing and the temperature of the molded product during use are close to the temperature indicating the maximum heat shrinkage stress (maximum heat shrinkage temperature). It is desirable to be temperature. Specifically, the processing temperature such as the RFL processing temperature and the vulcanization temperature in the adhesive processing performed as necessary is 100 to 250 ° C., and when the tire material generates heat due to repeated use or high speed rotation. Since the temperature can be as high as 100 to 200 ° C, the maximum heat shrink temperature is preferably in the range of 100 to 250 ° C, more preferably in the range of 150 to 240 ° C.

  The carcass ply 3 according to the present invention includes a fiber cord made of the above-described polyketone fiber and a coating rubber covering the fiber cord, and the coating rubber has various shapes as long as the PK fiber can be covered. Can do. Typically, it is a film, a sheet or the like. Further, as the coating rubber, a known rubber composition for carcass ply can be appropriately employed, and is not particularly limited.

  The PK fiber cord according to the present invention is coated with a rubber composition in accordance with a known method such as dipping, coating, and bonding to form a carcass ply. Such a carcass ply can have various PK fiber cord shapes, arrangements, coating forms, and the like.

(Preparation example of PK fiber)
A polyketone polymer with an intrinsic viscosity of 5.3, which is a completely alternating copolymer of ethylene and carbon monoxide, prepared by a conventional method is added to an aqueous solution containing 65% by weight of zinc chloride / 10% by weight of sodium chloride, and stirred at 80 ° C. for 2 hours. It melt | dissolved and obtained dope with a polymer concentration of 8 weight%.

  This dope is heated to 80 ° C., filtered through a 20 μm sintered filter, passed through a 10 mm air gap from a 50-hole nozzle with a diameter of 0.10 mmφ kept at 80 ° C., and 5% by weight of zinc chloride. Was extruded at a rate of discharge of 2.5 cc / min into water at 18 ° C. containing a coagulated yarn while being drawn at a speed of 3.2 m / min.

Subsequently, the coagulated yarn was washed with an aqueous sulfuric acid solution having a concentration of 2% by weight and a temperature of 25 ° C., and further washed with water at 30 ° C., and then the coagulated yarn was wound at a speed of 3.2 m / min.
The coagulated yarn was impregnated with IRGANOX 1098 (manufactured by Ciba Specialty Chemicals) and IRGANOX 1076 (manufactured by Ciba Specialty Chemicals) in an amount of 0.05% by weight (based on polyketone polymer), and the coagulated yarn was dried at 240 ° C. A finishing agent was applied to obtain an undrawn yarn.

A finishing agent having the following composition was used.
Oleic acid lauryl ester / bisoxyethyl bisphenol A / polyether (propylene oxide / ethylene oxide = 35/65: molecular weight 20000) / polyethylene oxide 10 mol addition oleyl ether / polyethylene oxide 10 mol addition castor oil ether / sodium stearylsulfonate / dioctyllin Sodium acid = 30/30/10/5/23/1/1 (weight% ratio).

  The obtained undrawn yarn was drawn at 240 ° C. in the first stage, followed by the second stage at 258 ° C., the third stage at 268 ° C., the fourth stage at 272 ° C., and then the second stage at 200 ° C. The film was stretched five times at 1.08 times (stretching tension 1.8 cN / dtex) and wound with a winder. The total draw ratio from the undrawn yarn to the five-stage drawn yarn was 17.1 times. Further, this fiber yarn had high physical properties such as a strength of 15.6 cN / dtex, an elongation of 4.2%, and an elastic modulus of 347 cN / dtex.

  In the following examples and comparative examples, in addition to the heat treatment conditions of the PK fibers in the above production examples, the PK fibers having the cord properties shown in Table 1 below by appropriately adjusting the twisting conditions and the dip treatment conditions of the cords according to ordinary methods Got. Each pneumatic radial tire (size: 33.0R51 E type) was prototyped by a conventional method according to the following Table 1 and the conditions shown below.

Each obtained tire was evaluated according to the following evaluation method.
(Cord weight)
The “weight” of the conventional example is set to 100, and is displayed as an index. A smaller number indicates a lighter weight.
(Driving durability)
The test tire (internal pressure: 700 kPa) was tested at a test speed of 8 km / h for a total time of 384 hours, with a test load of 150% of the maximum load specified by TRA (100%: 60 t) for 96 hours and 160%. The drum running test was carried out in stages with 96 hours, 170% for 96 hours, and 180% for 96 hours, and the length of the crack between the cords at the carcass winding end portion of the tire was measured for each tire. . For the laminated carcass ply, the largest value was the “crack length”. The “crack length” of the conventional example is set to 100, and is displayed as an index. The smaller the value, the better the running durability. The obtained results are shown in Table 1 below.

表中、カーカス総強力が○の場合、十分に実用に耐え得ることを意味する。カーカスプライに含まれるコード重量が○の場合、低燃費化および輸送費の抑制を図るに十分な軽量化がなされることを意味する。走行耐久性が○の場合、十分に実用に耐え得ることを意味する。

In the table, when the total carcass strength is ◯, it means that the carcass can sufficiently withstand practical use. When the weight of the cord included in the carcass ply is ◯, it means that the weight is sufficiently reduced to reduce fuel consumption and reduce transportation costs. If the running durability is ◯, it means that it can sufficiently withstand practical use.

From the test results shown in Table 1 above, the following was confirmed.
Example 1
A cord made of polyketone fiber having a dry heat shrinkage of 3% at 150 ° C. was applied to the carcass ply, and four carcass plies were laminated to form a carcass. By laminating four layers of carcass plies in this way, the in-layer cord gap and the total strength of the carcass equivalent to the steel cord of the conventional example can be secured, and both reduction in cord weight and running durability can be achieved. I was able to plan.

(Example 2)
A cord made of polyketone fiber having a dry heat shrinkage of 1% at 150 ° C. was applied to the carcass ply, and four carcass plies were laminated to form a carcass. By laminating four layers of carcass plies in this way, the in-layer cord gap and the total strength of the carcass equivalent to the steel cord of the conventional example can be secured, and both reduction in cord weight and running durability can be achieved. I was able to plan.

(Example 3)
A cord made of polyketone fiber having a dry heat shrinkage of 7% at 150 ° C. was applied to the carcass ply, and four carcass plies were laminated to form a carcass. By laminating four layers of carcass plies in this way, the in-layer cord gap and the total strength of the carcass equivalent to the steel cord of the conventional example can be secured, and both reduction in cord weight and running durability can be achieved. I was able to plan.

Example 4
Two inner-layer carcass plies in which a cord made of polyketone fiber having a dry heat shrinkage rate of 10% at 150 ° C. is applied to the carcass ply, and a cord made of polyketone fiber having a dry heat shrinkage rate of 5% at 150 ° C. in the carcass Two outer layer carcass plies applied to the ply were laminated to form a carcass. By laminating four layers of carcass plies with different dry heat shrinkage rates between the inner layer and the outer layer in this way, the inner-layer cord gap and the total strength of the carcass equivalent to the conventional steel cord can be secured. It was possible to achieve both weight reduction and running durability.

(Comparative Example 1)
A cord made of an aramid fiber having a dry heat shrinkage rate of 0% at 150 ° C. was applied to the carcass ply, and four carcass plies were laminated to form a carcass. By laminating four layers of carcass plies in this way, an inter-layer cord gap equivalent to that of the steel cord of the conventional example can be secured, but the cord cannot absorb the internal pressure diameter difference during manufacturing, so that distortion to the cord is not caused. As a result, the running durability decreased.

(Comparative Example 2)
A cord made of an aramid fiber having a dry heat shrinkage rate of 0% at 150 ° C. was applied to the carcass ply, and four carcass plies were laminated to form a carcass. As a result of the four carcass plies as described above, when the total strength of the carcass equivalent to that of the steel cord of the conventional example is ensured, the intra-layer cord gap is narrowed and the running durability is lowered.

(Conventional example)
This is a conventional example in which a steel cord is applied to a carcass ply and one carcass ply is laminated to form a carcass.

It is sectional drawing of the pneumatic radial tire for off-roads of an example of this invention.

Explanation of symbols

1 Off-road pneumatic radial tire 2 Bead core 3 Carcass ply 4 Reinforcement layer 5 Belt layer 6 Tread

Claims (5)

A carcass made of at least two carcass plies extending in a toroidal shape between a pair of bead cores, and a belt layer made of at least one belt ply arranged outside the carcass in the crown portion radial direction, In a pneumatic radial tire for off-road where at least one of the plies is composed of an organic fiber cord and a coating rubber formed by coating the organic fiber cord,
A pneumatic radial tire for off-road, wherein the organic fiber cord is made of a polyketone fiber cord having a dry heat shrinkage of 1 to 10% at 150 ° C.   The pneumatic radial tire for off-road use according to claim 1, wherein the polyketone fiber yarn has a tensile strength of 10 cN / dtex or more.   The pneumatic radial tire for off-road use according to claim 1 or 2, wherein the polyketone fiber base yarn has a tensile elastic modulus of 200 cN / dtex or more.   The pneumatic radial tire for off-road according to any one of claims 1 to 3, wherein the polyketone fiber cord has a dry heat shrinkage rate at 150 ° C of 4 to 7%.   The said carcass ply is 3-5 sheets, The pneumatic radial tire for off-roads as described in any one of Claims 1-4.

Images